1. Field of the Invention
The invention relates to a caller ID device, and in particular to a caller ID device with a power saving function by additionally using a current limiting circuitry and/or an FSK mark or space tone detector.
2. Description of the Related Art
A caller ID service that has been widely used in the North American countries can inform a user of the telephone number and the name of a calling party. Furthermore, with such a caller ID service provided, the user can be informed of the telephone number and the name of the calling party regardless of being at an off-hook state or an on-hook state.
Referring to FIG. 1, a conventional caller ID device 20 and a telephone 10 is shown. In FIG. 1, the conventional caller ID device 20 is electrically coupled to a pair of telephone lines (i.e., a tip terminal and a ring terminal) together with the telephone 10. The conventional caller ID device 20 includes a CAS (Customer Premises Equipment Alerting Signal) receiver 24, an FSK (Frequency Shift Keying) receiver 26, a controller 22, a voltage regulator 28, an LCD display 29, a DC battery 30 and an AC adaptor 32. Once the telephone 10 is switched into an off-hook state, the controller 22 detects an off-hook signal through a hook detector 12 of the telephone 10 and then outputs a control signal to activate the CAS receiver ready to receive a CAS signal from the pair of the telephone lines. If a CAS signal is coming from the telephone exchange through the pair of the telephone lines and received by the CAS receiver 24, the CAS receiver 24 outputs a CAS detecting signal to the controller 22. In response to the received CAS detecting signal, the controller 22 outputs a control signal to a speech network 14 of the telephone 10 to mute receiving and transmitting speech signals and another control signal to activate the FSK receiver 26 ready to receive an FSK modulated signal from the pair of the telephone lines. At the same time, a DTMF signal that represents a "D" signal with frequencies of 941 Hz and 1633 Hz is output from the controller 22 to the speech network 14 so as to inform the telephone exchange that FSK modulated data containing the telephone number and the name of a calling party can be send out. When the activated FSK receiver 26 receives an FSK modulated signal from the pair of the telephone lines, the FSK receiver 26 demodulates it into an FSK demodulated signal. Then, the FSK demodulated signal is outputted from the FSK receiver 26 to the controller 22 and then displayed on the LCD display 29.
On the other hand, when the telephone is switched into an on-hook state, the controller 22 detects an on-hook signal through the hook detector 12 and outputs a control signal to activate the FSK receiver 26 ready to receive FSK modulated data. Similarly, the activated FSK receiver can receive and demodulate an FSK modulated signal coming from the pair of the telephone lines into an FSK demodulated signal. Thereafter, the FSK demodulated signal is transmitted to the controller 22 from the FSK receiver 26 and then displayed on the LCD display 29. Typically, an on-hook data transmission FSK modulated signal consists of a channel seizure signal with a duration of 300 m sec, a mark signal with a duration of 50 m sec and a data signal in sequence as shown in FIG. 2, wherein the channel seizure signal is a dual-frequency signal having a mark frequency and a space frequency alternating at 1200 baud with each other.
In the conventional caller ID device 20, the CAS receiver 24 and the FSK receiver 26 are continuously activated once at an on-hook state and an off-hook state, respectively, resulting in more power consumption. Even though the AC adaptor 32 additionally used can last the life time of the DC battery 30, more power consumption caused by both the CAS receiver 24 and the FSK receiver 26 still exits.